This invention relates to mechanical fasteners and particularly to self mating mechanical fasteners.
Hook-and-loop fasteners (See for example, U.S. Pat. Nos. 2,717,437 and 3,009,235 both of which are incorporated by reference in their entirety herein) are in common, everyday use; but they still have important deficiencies. For example, the hook-and-loop composite is a relatively thick laminate, and can be conspicuous, e.g., in clothing applications. Further, loop material, especially in robust constructions, can be relatively costly. And opening or unfastening hook-and-loop fasteners can cause detachment of loops from their substrates, with a consequent generation of particulate debris. Additionally, the potential for particulate debris in hook-and-loop fasteners precludes their use in clean room environments and other areas where debris is destructive. Finally, the hook-and-loop type fasteners can involve a relatively complicated manufacturing process.
A wide variety of different fasteners have been taught as alternatives or replacements for hook-and-loop fasteners, including molded and extruded articles that have protruding inter-engaging elements having heads. See, for example, the fasteners described in U.S. Pat. Nos. 3,266,113, 4,290,174, 4,894,060, 5,119,531, 5,235,731, 3,586,220, 5,119,531, 5,888,621, 3,557,413, 6,106,922, 6,367,128 and PCT published application number WO 01/58780 all of which are incorporated by reference in their entirety herein. Many of these fasteners are self-mating, i.e., fastening is accomplished by interengaging fastener units of identical shape. In particular, many of the fasteners utilize protruding elements or xe2x80x9chooksxe2x80x9d, which are mounted to a first fastener portion and are spaced apart so as to provide a xe2x80x9creceptaclexe2x80x9d into which a mating element on a second fastener portion is forcibly inserted, thereby locking the two portions of the fastener in place.
This representative approach utilizing a profile-extruded self-mating film is shown in FIGS. 1 and 2. In this approach, two surfaces of ridge type hooks can be pressed together to make the hooks interlock. It is important to note that the ridges of hooks are equally and closely spaced, and that the hooks have a constant head width. The hooks are so closely spaced that two sheets of hooks cannot be pressed together without deforming the hooks as they slide past one another. This deformation of the hooks requires that the operator use force to xe2x80x9cclickxe2x80x9d the hooks into position. Without an engaging force capable of deforming the hooks, the hooks will not interlock and the fastener does not hold in place. Once interlocked, the hooks are pinned on either side by hooks from the opposing surface. Again, when two sheets of hooks are pressed together, they cannot be pulled apart without deforming the hooks, requiring a disengaging force.
This approach utilizes a constant head width of the hooks at nearly constant hook separation to control the engagement and disengagement properties of the hooks (and thus the interlocking portions of the fastener). The separation of the ridges can be described using a spacing-to-width ratio. This ratio is defined as the ratio of the center-to-center spacing of a stem portion of the ridges to the hook head width. If adjacent hooks having the same head width are disposed on a single sheet of film so that the heads abut, the center-to-center spacing of the ridges is equal to one head width, and the spacing-to-width ratio is 1. In another case, if two hook heads of equal head width have center-to-center stem spacing of a distance equal to their cumulative head width, the spacing to width ratio is 2.
A ratio of 2 defines the theoretical geometrical limit at which hooks from opposing planar sheets using the representative approach illustrated by FIGS. 1 and 2 may be spaced (assuming regularly spaced intervals) to engage or disengage normally. For ratios less than about 2, the hooks must deform as they engage or disengage.
In the representative approach indicated in FIGS. 1 and 2, the hooks deform during engagement and disengagement because the spacing to head width ratio is less than 2. As an example, one typical hook configuration has hooks spaced 50 mils apart with head widths 30 mils wide. The hook spacing to width ratio is 50 over 30, or 1.7. A large range in hook head width would be an increase or decrease of 3 mils. For the resulting 27 and 33 mil hook head widths, the spacing to width ratios are 1.9 and 1.5, respectively. Thus, for a large range of hook widths, the ratio varies by about 12% while still remaining less than 2.
The invention is a mating film. The mating film comprises a base sheet having a first major surface. A plurality of generally parallel ridges project from the first major surface. The ridges comprise a stem portion attached to the base sheet and generally upright from the base sheet. A head portion of each ridge is spaced from the first major surface and extends generally laterally from the stem portion so as to define a lateral distance. The center of each stem portion of each ridge is spaced from the center of each adjacent ridge stem portion by a distance greater than about 2 times lateral distance defined by the head portion.